A Zadoff-Chu (ZC) sequence is a complex-valued mathematical sequence which, when applied to radio signals, gives rise to an electromagnetic signal of constant amplitude, whereby cyclically shifted versions of the sequence imposed on a signal result in zero cross-correlation with one another at the receiver. A generated Zadoff-Chu sequence that has not been shifted is known as a “root sequence” (www.wikipedia.org).
These ZC sequences exhibits the useful property that cyclically shifted versions of itself are orthogonal to one another, provided, that is, that each cyclic shift, when viewed within the time domain of the signal, is greater than the combined propagation delay and multi-path delay-spread of that signal between the transmitter and receiver
The Physical Random Access Chanel (PRACH) is a process that facilitates the establishment of a link between mobile phones and a cell. A mobile phone that wishes to communicate with a cell selects a Zadoff-Chu sequence out of predetermined Zadoff-Chu sequences and transmits it to the cell, during a PRACH time window. If the cell does not detect, during the PRACH time window, the Zadoff-Chu sequence transmitted by the mobile phone that the mobile phone cannot communicate with the cell. The maximal number of Zadoff-Chu sequences that can be transmitted to the cell during the PRACH time window is a function of the coverage area (radius) of the cell. The search for the Zadoff-Chu sequence sis time and resource consuming and its duration may limit the maximal amount of Zadoff-Chu that can be successfully be searched during the PRACH time window and thus limit the coverage area of the cell.
There is a growing need to provide system and method for speeding up the search for Zadoff-Chu sequences during a physical random access channel search.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.